ULTRASONIC DEVULCANIZATION OF WASTE RUBBERS - EXPERIMENTATION AND MODELING

Continuous ultrasonic devulcanization of ground tire rubber (GRT) and styrene-butadiene rubber (SBR) is considered. Experiments are performe d under various processing conditions. Two recipes of SBR with differe nt amounts of polysulfidic linkages are utilized. Gel fraction and cro sslink density of devulcanized rubbers are measured and a unique relat ionship between them is established. Die characteristics with and with out imposition of ultrasonic waves are determined. Devulcanized sample s are revulcanized and mechanical properties are measured. In some cas es, properties of revulcanized SBR samples exceeded those of virgin vu lcanizates. This is explained based on the presence of a double networ k in the revulcanized rubber. A modification of acoustic cavitation an d flow modeling of ultrasonic devulcanization of SBR and GRT is propos ed using a concept of effective viscosity characterizing the flow of v ulcanized particles before devulcanization combined with a shear rate, temperature and gel fraction-dependent viscosity of devulcanized rubb er. Velocity, shear rate, pressure, and temperature field along with g el fraction, crosslink density and number of bonds broken are simulate d. Predicted data on gel fraction, crosslink density, and pressure usi ng the present modification of the model are found to be closer to exp erimental data then previously reported.